Field
The present invention relates to a semiconductor device including a SiN surface protective film and a method of manufacturing the same.
Background
Since GaN has a higher dielectric breakdown voltage than Si or GaAs, nitride semiconductor devices (GaN-based transistors) are devices expected to realize a high voltage/high output operation. An AlGaN/GaN heterojunction structure is typically known as a structure of nitride semiconductor devices.
However, in a region where the nitride semiconductor devices have a high operating voltage, a phenomenon called “current collapse” occurs in which a current decreases significantly during high-frequency operation. When current collapse occurs, output power which is expected to be obtained from DC characteristics cannot be obtained, and it is therefore necessary to suppress the current collapse.
Possible major causes for current collapse include temporary trapping of electrons in an impurity level and an interfacial level formed in an AlGaN crystal, a GaN crystal or on the AlGaN surface or the like during a high-voltage operation, and the occurrence of current constriction.
It is a known fact that applying SiN to a surface protective film drastically suppresses current collapse (e.g., see Fumio Hasegawa, edited by Akihiko Yoshikawa, “Wide Gap Semiconductor Optical/Electronic Device,” MOREKITA PUBLISHING, Co., Ltd. 2006, p. 245-246). However, since current collapse cannot be sufficiently suppressed by applying only SiN, a technique is disclosed which defines a SiN composition, film formation method and conditions and combination with other insulating films or the like (e.g., see JP 2009-10107 A, JP 2013-115323 A and JP 4912604 A). According to JP 2009-10107 A, SiN with excessive nitrogen (N) is used using an etching rate of a chemical solution as a main index. On the other hand, JP 2013-115323 A and JP 4912604 A focus on a SiN ratio and describe that SiN with excessive silicon (Si) is used.
However, according to JP 2009-10107 A, JP 2013-115323 A and JP 4912604 A, since no conditions for the SiN surface protective film that should be essentially satisfied to suppress current collapse are defined, there is a problem that it is not possible to obtain sufficient reproducibility with respect to the current collapse suppressing effect.